This invention relates to a magnetic recording apparatus and, more particularly, to the positioning of a magnetic head relative to a disc-shaped magnetic recording medium by projecting a light beam to the recording medium and, for example, a magnetic recording apparatus in which the output power of a positioning light for positioning the magnetic head may be increased.
A typical size of a recording medium attachable and detachable to a magnetic recording apparatus is 3.5 inch type which may have as high a track density as of about 2,100-2,500 TPI (Tracks Per Inch) and its recording capacity is 100-120 megabytes.
In order to enable recording, erasing or reproducing information of such a high recording density, the recording medium has been provided with a position detection track groove, so that a closed loop optical servo utilizing the position detection track groove can position a magnetic head in relation to the recording tracks.
FIG. 9 is an explanatory view indicating the optical system of a conventional magnetic recording apparatus. In the figure, 50 is a disc-shaped recording medium, 50a is a position detection track groove concentrically and continuously formed on one side of the recording medium 50 for a predetermined length, 50b is a cartridge portion for protecting the recording medium 50. 51 is a magnetic head for recording or erasing of information or reproducing the recorded information and is bonded to a support spring 51a to be mounted to the carriage mechanism portion (not shown) so that its magnetic gap portion (not shown) slides on the surface the recording medium 50 on the side to which the position detection track grooves 50a are provided.
Also, 52 is a light emitting and receiving portion, which is provided with a light emitting portion or a laser diode 52a (which will be referred to as LD 52a hereinafter) and a light receiving portion or a photo diode 52b (which will be referred to as PD 52a hereinafter).
Further, 53 is a hologram portion provided with an optical element (not shown) for separating the light from the LD 52a into a plurality of light beams and another optical element (not shown) for introducing the reflected light from the recording medium 50 to the PD 52b.
Also, 54 is a lens for focusing the light beams from the hologram portion 53 and for introducing the reflected light to the hologram portion 53, and 55 is a mirror for introducing the light beams from the lens 54 to the recording medium 50 and for introducing the reflected light beams from the recording medium 50 to the lens 54.
The components 52 to 55 constitute an optical system. This optical system, the magnetic head 51 and the support spring 51a are disposed on the carriage mechanism portion (not shown) so that they are simultaneously movable in the radial direction.
Its operation will now be described. The recording medium 50 is rotated at a constant speed by a medium drive motor (not shown). The magnetic head 51 is supported by the support spring 51a so that its magnetic gap portion slides over the recording medium 50.
The closed loop optical servo control will now be described. The light emitted from the LD 52a is divided mainly into three light beams through the hologram portion 53, and these three light beams are focused by the lens 54 and directed to the mirror 55 as three light beams. The mirror 55 guides these light beams onto the recording medium 50.
When three light beams are to be irradiated to the position detection track groove portion 50a, the position of the light emitting and receiving portion 52 is adjusted during assembly of the apparatus so that the direction of alignment of the three light beams defines a predetermined angle with respect to the position detection track groove portion 50a.
The three light beams directed to the recording medium 50 by the mirror 55 are reflected as the reflected light beams of different intensities according to the irradiated state relative to the recording medium 50 or the position detection track groove portion 50a disposed on the recording medium 50. The three light beams reflected to the mirror 55 are directed to the lens 54 by the mirror, fed to the hologram portion 53 by the lens 54, and applied to the PD 52b through the hologram portion 53.
The PD 52b receives three deflected light beams and provides detection signals in accordance with the intensity of the received light. The servo control portion (not shown) receives the detection signal from the PD 52b and delivers a drive signal for driving the carriage mechanism portion (not shown) in accordance with the content of the detection signal. The closed loop optical servo control continues until the magnetic head (more precisely, the magnetic gap portion) in the carriage mechanism portion is assigned to a predetermined track.
Since the conventional magnetic recording apparatus has the structure as above described, three light beams must be precisely focused on the recording medium 50 (or the position detection track groove 50a). The focus point preciseness of the light requires .+-.50 .mu.m and this focus adjustment requiring .+-.50 .mu.m is typically achieved by adjusting the position of the lens 54. However, the hologram portion 53, the lens 54, the mirror 55 and the like are separate components, so that their relative position must be finely adjusted and that the tilt of the lens must also be taken into consideration, resulting in a difficult focus point adjusting operation.
Also, the aligning of the light axis with respect to the position detection track groove portion 50a for a precise signal detection by the light emitting and receiving portion 52 has been very difficult in the past because the light emitting and receiving portion 52, the hologram portion 53, the lens 54 and the mirror 55 are separate components.
Also, since the hologram portion 53, the lens 54, the mirror 55 and the like are separate components, their positional adjustment is difficult and it is difficult to make the optical system small and thin, thereby preventing the magnetic recording apparatus from being made small and thin.
Japanese Patent Laid-Open No. 4-219640 discloses, although not in the field of the magnetic recording apparatus, techniques for integrating an optical system into the hologram portion. However, since these techniques are not the technique in the field of the magnetic recording apparatus, it is difficult to irradiate the light beam onto the position detection track grooves 50a on the recording medium 50 precisely at the proper angles because the surface of the recording medium 50 vibrates due to the sliding movement of the magnetic head 51 thereon, requiring other components such as mirrors, lens and the like, which makes the focus adjusting operation further difficult.
Also, in the apparatus in which the optical system is integrated into the hologram portion, in order to make the light beam travel in a zig-zag manner within the inside of the hologram, opposing surfaces of the hologram made of polyolefin system plastic has formed thereon reflection surfaces of aluminum deposited in a vapor. However, such reflection surfaces of aluminum are not satisfactory for obtaining a positioning light beam and a reflection light beam having a sufficient output intensity. That is, in the magnetic recording apparatus in which the magnetic head 51 slides over the recording medium 50, the reflection factor of the recording medium 50 used is not inherently required to have a high reflection factor, so that the reflection factor is not as high as that of the recording medium (not shown) used with the optical recording apparatus (not shown). In the magnetic recording apparatus, a high output intensity is required for the positioning light and this positioning light of the required output intensity cannot be obtained through the use of an aluminum reflection surface so that the magnetic head 51 cannot be positioned on the desired recording track. Also, due to the relationship of the light reflection or absorption characteristics of aluminum with respect to the light wavelength or output emitted from the light emitting portion, sufficient light output cannot be obtained.